ADVANCEMENT OF STRUCTURAL SAFETY AND SUSTAINABILITY WITH ... Papers/Wu.pdf · ADVANCEMENT OF STRUCTURAL SAFETY AND SUSTAINABILITY. WITH BASALT FIBER REINFORCED POLYMERS. Wu Zhishen

ADVANCEMENT OF STRUCTURAL SAFETY AND SUSTAINABILITY

WITH BASALT FIBER REINFORCED POLYMERS

Wu Zhishena,b

, Wang Xina, Wu Gang

a

a International Institute for Urban Systems Engineering, Nanjing 210096, China

b Department of Urban and Civil Engineering, Ibaraki University,Hitachi,316-8511, Japan

Abstract：Basalt fiber composites (BFRP) have been receiving increasing attention in civil infrastructures,

due to their excellent mechanical and chemical properties and high cost-performance. This paper reviews

the recent achievements in advancing structural safety and sustainability by BFRP composites based on the

research conducted by the authors’ research team. The major research consists of the advancement of basalt

fibers through enhancing production techniques, the fundamental study of BFRP under static and cyclic

loading, high temperature and severe environment and the common application directly by BFRP products.

To further pursue the advantages of BFRP and its application in safe and sustainable structures, the

advancement of BFRP composites through hybridization with other materials is also addressed. Based on

the advancement in BFRP composites, the innovative application techniques of BFRP in civil

infrastructures are further introduced, including smart structures with BFRP smart bars, long-span bridges

with hybrid BFRP cables, the prestressed concrete structures with pre-tensioned BFRP sheets, damage

controllable and recoverable structures with SFCB, and the sustainable structures with BFRP profiles.

Finally, some new directions of research and future application for the enhancement of structural safety and

sustainability are proposed.

Keywords: basalt fiber, FRP, safety, sustainability, advancement

1. Introduction

In recent years, increasing attention has been paid to structural safety and sustainability, which includes

structural durability, the lightweight requirement, the recoverability after disasters and the related

economical and recyclability issues. For instance, a steel truss bridge on (I-35W), with only 43 years of

service, in Minnesota USA collapsed entirely in 2007[1]

due to the fatigue and corrosion of a joint; the

self-weight accounts for 85% of the total stress in structural members of high-rise buildings; the financial

losses due to corrosion of structures by ocean water reaches 700 billion USD globally and 100 billion USD

for China every year [2]

; and it is reported that the steel mine reserve in China is only 11.5 billion tons, but

the exploitation is reaching more than 0.6 billion tons each year. All these problems which pose a potential

crisis, indicate that the durability of structures need to be greatly enhanced and in order to improve

structural safety keep, and the self-weight of structures should be lowered to reduce stresses in structural

members and to extend the structural lives , and the recoverability of structures should be improved in

order to ensure quick recovery of major constructions after large disasters such as earthquake and blast.

To address the solve above problems, a promising solution is offered by using fiber-reinforce polymer (FRP)

composites, which have clear advantages such as high strength, light weight, good resistance to fatigue and

corrosion, ease of forming, and etc, in comparison with steel elements [3-5]

. Partial or complete adoption of

FRP composites as structural members can significantly enhance structural safety and sustainability.

Effectiveness of this approach has been widely demonstrated in the world within the last thirty years.

Basalt FRP (BFRP) is the latest FRP composite that has developed within the last ten years and has been

Proceedings of CICE 2012 6th International Conference on FRP Composites in Civil Engineering Rome, Italy, 13-15 June 2012 © International Institute for FRP in Construction (IIFC)

proven to have advantages in achieving the goal of enhancing safety and reliability of structural systems

compared with the conventional carbon, glass and aramid FRP composites. CBF (Continuous Basalt Fiber)

is an inorganic fiber and functional material. It is also a typical energy saving, environment-friendly, natural

green fiber. Along with carbon fiber, aramid fiber, and high molecular polyethylene fiber, CBF is becoming

China's fourth high-tech fiber. CBF has many unique excellent behaviors[1]

, such as good mechanical

properties, a wide-range of working temperature (-269~700 ℃), acid, salt and alkali resistance, anti-UV, low

moisture absorption, good insulation, anti-radiation, and sound wave-transparent properties[6]

. BFRP

composites have begun to be used in national defense industry, aerospace, civil construction, transport

infrastructure, energy infrastructure, petrochemical, fire protection, automobile, shipbuilding, water

conservation and hydropower, ocean engineering and other fields.

Fig.1 Stress-strain relationship of different FRP

BFRP shows advantageous characteristics in mechanical, chemical and high ratio of performance to cost in

comparison to CFRP, GFRP, AFRP, steel bars, and etc, as shown in Fig.1. For instance, BFRP has a higher

strength and modulus, a similar cost, and more chemical stability compared with E-glass FRP; a wider

range of working temperatures and much lower cost than carbon FRP (CFRP); over five times of strength

and around one third of density than commonly used low-carbon steel bars.

Due to above advantages, BFRP has already become an attractive alternative for replacing conventional

construction materials and is expected to enhance structural safety and sustainability. However, although

BFRP has potential advantages, as mentioned above, the fundamental studies and the relevant applications

are still limited due to the relatively recent development compared with other FRP composites. Focusing on

identifying the deficiencies, the authors’ research team has conducted a series of studies to develop a more

in-depth understanding of the fundamental behavior, the strengthening mechanism, and the application

technologies of BFRP composites. In particular, herein some enhancement techniques, which are used for

improving the properties of BFRP are studied with regard to structural safety and sustainability

requirements. In this paper, the fundamental studies on basalt fibers and BFRP are first summarized; the

practical applications of BFRP in civil infrastructures are then introduced; the progress in BFRP with a

focus on structural requirements is further addressed. Finally, some key and innovative application

technologies for achieving high-performance and durable structures are presented.

2. Fundamental study of basalt fibers and composites

2.1 Basalt fibers[6-7]

Although basalt fibers and composites have potential advantages for application in construction, compared

with conventional structural and the other fiber materials, there are several issues and major challenges that

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still limit their further development and applications. Among these are stability, ability of large scale

production, lack of high-end products and special types of basalt fibers. The stability of the mechanical

properties of basalt fibers is the most important issue, because the unstable properties greatly lower the

utilization efficiency leading to a waste of material and subsequently, limited applications in engineering.

Due to this present limitation, the basic requirement for basalt fiber sheet is a strength larger than 2000

MPa and the CV less than 5%. The mass production is also a key factor for lowering the cost and thus,

widening the application fields of basalt fibers, which is currently limited by the production equipment and

the related production technologies. Basalt fibers should not only be regarded as a superior replacement of

glass fibers, but it is also possible to develop high-end basalt fibers that can exhibit similar behavior to

carbon fibers (T-300) in order to meet different structural requirements. Meanwhile, it is possible to

develop special types of basalt fibers for hazard mitigation and extreme condition applications, such as

high-temperature (fire) resistant structural materials, materials for severe environments (acid, alkali), and

other structural engineering applications that require a high level of safety, risk mitigation and reliability.

To overcome the barriers that currently limit the utilization of Basal Fibers to be utilized in such wide range

of applications, a series of studies is currently on-going with a focus on the production process of basalt

fibers as shown in Fig.2 [5]

.

The first is the development of the proper technology for mineral selection. It should be mentioned that

CBF requires strict chemical and mineral compositions, and thus, not necessarily any Basalt mine can be

used to produce CBF. Thus, the mineral selection technology is the base for producing basalt fibers. This is

currently limited due to the following bottleneck problems: high temperature of devitrification, fast speed

of revivification and cooling, narrow temperature range of fiber formation, and high content of Fe, and poor

diathermancy of melting. At present, the technology development is studied through investigating chemical

and mineral composition.

Fig.2 Key technologies for enhancement of basalt fibers

The second is mineral melting and drawing technology. In order to obtain homogeneous melting, an

automatic feeding device was developed by this research team to precisely control the feeding of basalt and

to avoid shortcomings of hand feeding. A level controller was designed to optimize the melting process. By

称量称量

连续玄武岩纤维的生产流程图连续玄武岩纤维的生产流程图

玄武岩矿石玄武岩矿石

烘干烘干原丝原丝

拉丝机拉丝机

浸润剂浸润剂

加料机加料机

窑前料仓窑前料仓

粗纱粗纱

细纱细纱

其它制品其它制品

Basalt mine Feeder

furnace

Surface treatment

drawbenchroving

yarn

Other products

stranddrying

weighing

Natural occurring material, unstable

Intelligent selecting technology

single pot furnace-low producing capacity

Advanced monitoring/control

technology

Surface treatment study

just started

Specially for basalt fibers

单元炉，产量低，生产工艺不稳定

高度监控技术

Drawing tech needs

further

improvement

Auto equipment

Under

development: 800、1200、1600-hole

drawbench

bushing


utilizing this approach, intelligent monitoring and control technology can be realized. Due to the

importance of bushing plate, lubricator, gathering roll and traverse unit, their positions greatly influence the

stability of drawn fibers. Thus, a series of parameters that control the positions were studied, which resulted

in an optimization of drawing technology and the enhancement of the quality of basalt fibers.

The third is the surface treatment (sizing) technology. The surface treatment through film forming agent,

lubricant, coupling agent will greatly influence the behavior of fibers and the matrix. The studies were

conducted according to the certain requirements of construction such as the behavior under elevated

temperatures and bonding behavior of fibers and matrix under corrosive environment. Now, the lack of

high performance sizing raw material is a limitation to improve surface behavior.

The fourth is the mass production technology. To realize massive production and subsequently lower the

cost, a transition from single crucible furnace to tank furnace was studied. The optimization of the electrical

furnace, the design and development of electrical-gas furnace and large-scale bushing (800 -1600-hole

drawbench bushing) are the key issues.

Through above studies, the mechanical and chemical properties of basalt fibers can be enhanced based on

the application requirements, which means the structural performance can be designed and controlled the

level of source materials first. The above studies will provide wider and more flexible choices of basalt

fibers for structural application.

2.2 Basic properties and regular applications of BFRP

2.2.1 Types of BFRP products

To satisfy different structural applications, various types of basalt FRP products were developed in the

recent years. The basalt fiber roving (Fig.3(a)), unidirectional sheets (Fig.3(b)) were first developed and

widely used. In the last six years, the research team developed a variety of basalt FRP products [8]

(shown

in Fig. 3) such as (c) grids, (d) laminates, (e) bars, (f) profiles, and some advanced products including (g)

smart bar embedded with fiber optic sensors, (h) steel-fiber composite bar (SFCB), (i) fiber-steel wire FRP

plate, (j) hybrid FRP tendons, (k) high temperature durable FRP plates, (l) basalt fiber sandwich structure

member etc.

(a) (b) (c) (d) (e) (f)

(g) (h) (i) (j) (k) (l)

Fig.3 Basalt fiber composite products

2.2.2 Basic mechanical properties

The typical mechanical properties of basalt fiber sheets are shown in Fig.1, in which the strength and the

elastic modulus of basalt fiber sheets have increased over the recent years by improving production

technologies (Fig.4), and have reached around 2100 MPa and 90 GPa at present. The strength and modulus

are 1350 MPa and 55 GPa, for the basalt FRP tendons with vinyl ester, and 1500 MPa and 50GPa for the

tendons with epoxy resin. The strength of BFRP grids is larger than 1000 MPa compared with GFRP grids


with 600 MPa and CFRP grids with 1400 MPa.

（a）tensile strength （a）elastic modulus

Fig.4 Mechanical properties of basalt fiber sheet between 2005-2010

2.2.3 Fatigue properties of BFRP

As considerable civil and transportation infrastructures are under the cyclic or dynamic loads, for instance,

the bridge decks, large-span bridge girders, roads, cables, etc. are subjected to frequent traffic loads and

wind loads, thus, the use of FRP materials in these structures or construction facilities, requires that their

resistance to fatigue must be guaranteed to meet the safety requirements. The research team tested the

fatigue behavior of BFRP sheets under different stress levels [9]

. The results show that BFRP sheets are able

to maintain the maximum cyclic stress of 55% (amplitude R=0.1), without fracture, subjected to two

million cycles of loading. So, in general, the fatigue strength of BFRP can meet the requirements of the

majority of engineering facilities.

Fig.5 Modules degradation with cyclic loading

In addition to fatigue strength, a change of the tensile module of BFRP is recorded in the experiment as

shown in Fig.5. The damage represented by the reduced modulus was permanent. The fatigue failure of

tested sheets, thus, occurred when the total accumulated damage reached a critical limit. Although there

were notable scatters in the modulus reduction, the critical limit was approximately 75% to 90% of the

initial modulus of BFRP sheets. Thus, the reduction of elastic modulus of BFRP should be further

investigated to ensure structural deformation requirements.

2.2.4 Tensile properties of BFRP under elevated temperatures

The structural safety under sudden disaster, such as fire which is a commonly occurring disaster, is

always an important topic of concern in civil and transportation engineering.. In comparison to

conventional structural materials such as steel and concrete, BFRP composites are relatively week in

resisting high temperature. Thus, it is extremely important to design a structure with FRP which can

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guarantee the performance under the high temperature environment and evaluate the effect of residual

strength of BFRP to structural safety. In addition, it is also a major concern whether toxic gases are released

from the FRP composites subjected to fire. To address the above problems, the tensile property of BFRP

bar (8mm in diameter and 60 vol% of fibers) pultruded with a vinyl ester has been verified under the

temperature up to 300℃. The results (Fig.6) show that the bar was able to maintain about 85% of its tensile

strength due to the high Tg of vinyl ester (around 120 C). It is also indicated that the pultruded FRP has a

better homogeneity and can achieve higher residual strength.

Fig.6 Tensile strength of basalt FRP bars

To further clarify the mechanism of tensile degradation of BFRP under elevated temperatures, the basalt

fiber bundles were tested under the temperatures up to 500℃, subjected to different conditions, tension

under heating and after heating. The degradation of tensile strength of basalt fibers is shown in Fig.7, which

shows in general, below 200 ℃ the tensile strength stays constant and gradually decreases between 200

and 300 ℃, and noticeably drops after 300℃, and finally reaches the minimum at 500℃. The degradation

of strength under tension while subject to heating is faster than when it is under tension and the temperature

has exceeded 300℃. This phenomenon shows that no damages on fibers can be caused under 200℃ and

the damage can be accumulated and accelerated with the elevation of the temperature after 200℃. In

general, the tensile strength of basalt fibers degraded faster when they were tensioned under heating

compared with those tensioned after heating. Besides the test of basalt fibers under the temperatures up to

500℃, the BFRP bars with diameters of 6 mm were also tested. The strength degradation is also shown in

Fig. 7 in compassion with those of basalt fibers. The degradation trend of BFRP is similar to that of basalt

fibers under elevated temperature, which indicates that the state of fibers in the FRP mainly controls the

overall strength of FRP.

Fig.7 Strength degradation of basalt fibers and BFRP bars

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Tg=120ºC Td=355ºC


Fig.8 Comparison of strength degradation among different types of materials

The strength degradation of the aforementioned tested BFRP bars with 6-mm and 8mm diameters are

also compared with those of CFRP, AFRP, GFRP and steel bar referred from [10-11]. The results show

among different FRP bars, BFRP bars exhibit superior high strength retention within 300℃, which is

similar to the performance of steel bars and CFRP, and much better than that of GFRP and AFRP bars.

However, the limitation that BFRP bars almost lose their strength under the temperature of 500℃ still

should be investigated thoroughly.

2.2.5 Properties under severe environment

(1) Under freeze-thaw cycles

In order to evaluate the mechanical properties of basalt FRP under severe environment (such as in North

China, Northwest Territories, as well as coastal areas), the research team tested the mechanical properties of

BFRP sheet under the freeze-thaw cycles [12-13]

, meanwhile, references [14]

tested the mechanical properties

of carbon fiber and glass fiber under the same conditions. For comparison three types of FRP are presented

in Fig. 9. The results shows that no obvious change was found in failure mode between the exposed

coupons and the controled ones. The ultimate strength of CFRP and GFRP sheets decreased continuously

with the increasing cycles, while BFRP sheet decreased slightly before 100 cycles and later increased.

Freeze-thaw cycles did not affect the modulus of elasticity of these three FRP sheets. The ultimate strain of

CFRP and BFRP sheet fluctuated with the increasing cycles and BFRP sheet showed a higher retention rate

than CFRP and GFRP sheets under high freeze-thaw cycles.

（a）tensile strength (b) elastic modulus (c) failure strain

Fig.9 Comparison of BFRP, CFRP and GFRP under freeze-thaw cycles

(2) Under alkali solution

BFRP applied in RC structures is usually affected by the alkali action due to its embedment inside the

concrete. To evaluate the alkali effect on the BFRP reinforcement, accelerated aging tests are conducted to

verify the mechanical degradation. The test specimens included BFRP bars (a diameter of 6mm) with vinyl

ester resin which is under 55℃ alkali solution with a PH value of 13. The experimental results are shown in

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Steel bar

BFRP rebar

6mm BFRP Bar

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Fig.10, which are also compared with the alkali resistance performance of E-glass and T-glass FRP rods [15-17]

.

Fig.10 Degradation of BFRP, E-glass and T-glass FRP

Results show that the initial strength degradation of basalt.vinyl ester is similar to that of E-glass/polyester

and T-glass/ripoxy, but faster than that of the E-galss/vinylester due to the influence of the diameter of the

bar. It is also shown that after initial degradation, the strength degradation rate of balsalt/vinylester is

obviously slower than the other FRP rods. In this regards, it is concluded that BFRP should have stronger

resistance compared to E-/T-glass FRP. But more experiments of BFRP should be conducted to develop

prediction model.

(3) Properties under salt solution

The corrosion due to salt is usually occurred under coastal environment which is directly affecting the FRP

reinforcement such as cables. Considering the actual load condition of those FRP reinforcements, the

prestress load is considered in the evaluation of their behavior under salt solution. The 6 mm diameter

BFRP bars with vinyl ester under the room temperature were tested.

The degradation of BFRP with regard to the aging days subjected to different levels of stress ratios is

shown in Fig. 11(a). Overall, the retention of tensile strength of BFRP tendons remains high (over 90% of

tensile strength) independent of the curing days and the stress levels. This demonstrates BFRP tendons

can resist saline corrosion in different applications such as stay cable or external prestress cables. The

apparent drop of strength can be found within the initial thirty days, after which the degradation rate is

lowered. It os also apparent that with the higher level of stress, the degradation of tensile strength is larger,

whereas the amplitude of strength degradation between the tendons subjected to pres=0 and pres=0.3fu is

larger than that between the tendons under pres=0.3fu and pres=0.6fu. This phenomenon indicates that, on

one hand, the applied stress aggravates the degradation of BFRP tendons. This can be interpreted that the

stress in FRP contributes to the propagation of micro-cracks in the matrix, which make corrosive ions

easier to penetrate into the matrix and damage the interface between the fibers and the matrix. On the other

hand, the contribution of high stress to degrade the tensile strength is nonlinear, which means the

propagation of micro cracks is more sensitive to the initial stress rather than the higher stress.

20%

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100%

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Basalt/vinylester rod, 6mm,55C (Wu)

E-glass/ployester rod,6.35mm, 60C (Micelli,Nanni)

E-glass/vinylester rod,9.53mm, 60C (Chen)

T-glass/Ripoxy-R802 rod,6mm,40C (Uomoto)


(a) Tensile strength degradation (b) Variation of elastic modulus

Fig.11 Strength degradation of BFRP tendons under salt solution

Although the differences of modulus variations are identified as shown in Fig.11(b), it is still difficult to

figure out a distinct trend of variation of modulus due to the overall small amplitudes (less than 3.5%). This

small amplitude of variation indicates the salt solution has slight effect on the degradation of modulus and

indirectly demonstrates that the corrosive elements mainly affect on the matrix and the interface between

the matrix and the fibers.

2.2.6 Typical engineering applications for BFRP

Above BFRP products have been used in various infrastructures and gradually prove their advantages in

integrated high performance applications. Some regular and typical applications in civil infrastructures are

introduced as follows.

(1) Chopped basalt fiber-reinforced asphalt pavement [18]

With the increasing development of road transportation in China, the traffic volume and axis load continues

to increase. The requirements for the high quality and longer service life of the asphalt pavement are also

becoming more strict. As more new materials are used in the asphalt pavement technology, adding fiber in

the asphalt mixture for enhancing the performance of asphalt mixture becomes an important tool. Fibers in

the asphalt mixture exist in three-dimensional dispersed phase and overlap each other, which can avoid

over-concentration of load and improve the overall strength of asphalt mixture; meanwhile, the water

stability and high temperature stability of asphalt mixture are improved because of the absorption effect of

fiber to the mixture.

The most commonly used fibers in the asphalt concrete pavement engineering are lignin fibers, polyester

fibers, mineral fibers and basalt fibers. Basalt fiber is becoming a highly competitive product compared

with the other fibers because of its desirable mechanical properties and high temperature performance.

Fig. 12 and Fig. 13 show that the anti-water-damage performance of BFRP asphalt mixture is slightly

higher than the polyester asphalt mixture and the asphalt mixture, and the high-temperature stability is

improved significantly.

90%

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浸水马歇尔稳定度试验

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不加纤维玄武岩纤维1 玄武岩纤维1 聚酯纤维1 聚酯纤维2

残留

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%）

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fiber 1

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fiber 2Polyester

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fiber 2

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Fig.12 Water immersion Marshall stability test Fig.13 High temperature stability test

Recently, Hangjinqu Highway K143 +512 ~ K144 +141 section incorporated basalt fibers made by of

Zhejiang GBF Basalt Fiber Co., Ltd. to strengthen the AC-13 modified asphalt concrete, and carried out

overlay conservation tests. After overlay construction, the overall conditions of these sections have

improved, for instance there is no presence of oil on the surface and no loose phenomenon. Based on the

core taken from the onsite condition, the compaction degree are up to 99%, and the water permeability

coefficient and anti-slip values can all meet the specification requirements. Using the basalt fiber modified

asphalt concrete AC-13 to deal with the road maintenance can improve the conservation quality and service

life of the pavement This results in low afterward maintenance costs and great economic benefit.

(2) Chopped basalt fiber reinforced concrete [19-20]

The basalt fiber can be used in the tunnel and underground engineering by taking advantage of its high

strength and fire proof properties. Southwest Jiaotong University and Zhejiang GBF Basalt Fiber Co., Ltd.

conduct the research about the basalt fiber shotcrete. It has been proved that the basic mechanic properties

of the basalt fiber shotcrete have met the quality requirement of concrete. The compressive strength, the

shear strength and the flexural strength have all been greatly improved comparing to the plain concrete. The

impermeability coefficient of the basalt fiber concrete and the basalt fiber composite concrete are all

achieve the level S12. The shotcrete tests show that the basalt fiber have an obvious effect on the rebound

of steel fiber, it reduces the rebound rate and improve the utilization rate of the steel fiber in the shotcrete.

The project researcher believes that the basalt fiber with length range of 20~25mm and diameter range of

18~22μm and the steel fiber can be applied in the tunnel lining through optimized combination. It is

recommended that during the design and construction process, the volume of basalt fiber and steel fiber

should be choose by considering the onsite geological environment and load condition. If you want to

increase the toughness results, we recommend adding an appropriate amount of steel fiber.

Basalt fiber can be used as a construction material to delay the crack propagation due to the early shrinkage,

and the compatibility between the concrete and basalt fiber is very good. Unlike the steel fiber, the basalt

fiber in the concrete will not affect the insulation property of the prestressed concrete; also it will not

corrode like steel fiber, which makes the basalt fiber an ideal admixture to the Ballastless track slab. There

are two slabs already been used in the Passenger Dedicated Line from Wuhan to Guangzhou and they have

participated in the on-site condition test from 2008 as show in Fig.14.

Fig.14 Ballastless track slab with basalt fibers

(3) BFRP bars for non-magnetic structure [21]

The elastic modulus of the BFRP bar is relatively low (currently about 55GPa) compared to

conventional steel, but it has some obvious advantage in some application areas due to its low price,

non-rusty, electrical insulation, non-magnetic, acid and alkali resistance properties. For example, in 2007 in


order to meet the seismostation’s non-magnetic requirements, Lanzhou Seismological Bureau uses BFRP

bars instead of steel bars in the construction of seismostation (Fig.15). Southeast University developed the

bending manufacture technology in order to solve the reinforcement bending and stirrup making problem.

The seismostation works well at present.

Fig.15 BFRP bars in Lanzhou seismostation

In May 2008 the Southeast University, Zhejiang GBF Basalt Fiber Co., Ltd. and Zhang Shi Shijiazhuang

highway management jointly develop a continuous reinforcement construction technology using BFRP

reinforcement to enhance the road, taking north and south ends of the Xingtang Bridge for the trial (Fig.16).

This continuous reinforcement construction technology achieve a truly non-welded connection, reducing

the shrinkage cracks of the concrete blocks, it also resolve the corrosion effect of the de-icing salt

compared to the steel reinforcement, which improve the quality and durability of highways and reduce

highway costs, shorten construction time.

Fig.16 Application of BFRP bars in highway construction

(4) Structural seismic strengthening

Because the priority concern of structural seismic strengthening is ductility rather than strength and

stiffness, basalt fiber sheet have a unique advantage comparing to the carbon fiber sheet in this area. The

research team performed comparison test between BFRP and CFRP wrapped column [22]

. Fig. 17 shows the

testing hysteresis curves of the columns with no strengthening, with 2.5 layers of wrapped CFRP, with 4.5

layers of wrapped CFRP and with basalt fiber bundle circle around the columns, which are represented by

S-0, S-2.5C, S-4.5C and S-BF respectively. The tests results show that the column strengthened by basalt

fiber bundle shows much higher of shear strength compared to the others, and the basalt fiber bundle can

also change the failure mode of the column. Under the similar lateral restraint stiffness, the continuous

basalt fiber sheets strengthened columns can achieve the same or higher strength, energy dissipation and

ductility but lower price than CFRP strengthened columns. Thus, the BFRP is more suitable for structural

strengthening with higher seismic performance.


Fig.17 The load-displacement curves of concrete columns before and after strengthening

(5) Underwater strengthening with BFRP grids

Offshore infrastructures encounter severe natural surroundings like chloride attack, tsunami, tidal waves,

earthquake, etc. Reinforcement concrete and steel structures are vulnerable in severe environments, which

may damage their durability and load carrying capacity. Also, the cost for regular inspection and repair is

tremendous. Considering the particularity of strengthening underwater structures, bonding and curing are

two significant concerns. It is usually difficult for FRP sheets to bond evenly on the surface of underwater

concrete elements due to the influence of water. For this sake, the application of FRP sheet strengthening

underwater structures is restricted. Therefore, the special BFRP grids have been exploited to solve this

problem. The procedure of strengthening underwater column with BFRP grids is shown in Fig.18. The first

step is to treat the concrete pier’s surface, and then paint it with an underwater type of epoxy resin to a

thickness of about 2 mm. After, BFRP grids are bonded to the surface by pressing them into the adhesive

layer. In the last step, the epoxy is re-painted to a total of 5 mm thick.

Fig.18 Underwater strengthening with BFRP grids

Lateral Displacement (mm)

-45-40-35-30-25-20-15-10 -5 0 5 10 15 20 25 30 35 40 45-800

-600

-400

-200

0

200

400

600

800

S-0S-2.5C

Lat

eral

Load

(kN

)

-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45

-800

-600

-400

-200

0

200

400

600

800

S-4.5C

S-BF

Lat

eral

Lo

ad (

kN

)

Lateral Displacement (mm)

Underwater type epoxy

BFRP grid

Superstructure

Strengthening layer

Substructure


The sufficient bonding capacity between BFRP gird and concrete surface has been obtained through

single-lap shear and three-point loading tests, whereas the same magnitude of capacity has been obtained

with BFRP grids, which only have 70% fibers compared with BFRP sheets.

(6) BFRP sandwich structures

The structures facing impact and explosion loads are becoming more prominent. It is needed to develop

new materials and new structures with integrated high performance. From previous experience, it is not

recommended to rely solely on increasing the structure size to improve its disaster preparedness; the use of

porous lightweight materials in design of the structure has become a research hotspot in explosion area. The

currently most typical porous lightweight material is the sandwich structure. Sandwich structures are

usually composed by an upper panel, a core material and a down panel. The panel materials require for

good stiffness and strength, the commonly used materials are FRP, aluminum, steel, concrete etc. The basalt

fiber used as the panel has a low price, light weight, good adhesion, and excellent corrosion resistance etc.

The research team proposed basalt fiber reinforced polymer-lightweight aerated concrete (BFRP-ALC)

sandwich structure (Fig. 19). This new type of sandwich structures can be widely not only used in the fields

of fortification, civil air defense engineering and defense engineering, but also in bridge engineering,

industrial and civil construction and other fields. The research team has already conducted preliminary

testing and verification and the results are satisfactory [23]

.

Fig.19 BFRP sandwich structure

3. Advancement of BFRP composites

Due to the structural multi-requirements including capacity, stiffness, ductility, stability and economy, one

kind of FRP usually cannot satisfy above needs due to their relatively simplex advantage. For instance,

BFRP has high tensile strength but its relatively low elastic modulus usually causes structural stiffness

deficiency such as stay cables in cable-stayed bridge. Another example is simply use BFRP in RC structure,

the ductility and recoverability are difficult to control due to its linearity of stress-strain relationship.

Focusing on above limitations, a hybrid design concept was adopted and developed for achieving integrated

high-performance basalt fiber based FRP composites [24]

.

3.1 Design and advancement of basic mechanical properties

Three types of hybridization are adopted in the study to meet different structural requirements, as shown in

Fig.20(a). It shows an idealized stress-strain relationship of hybrid FRP consisted of three types of fibers,

high modulus, high strength and high ductility. High modulus fibers are designed to ensure the

enhancement of initial stiffness. The mixture of high modulus and high strength fibers presents a certain

strain hardening behavior until the rupture of the high strength fibers, which may be used to control the

deformation of structures with a good recoverability. In addition, the ductility can be guaranteed by mixing

with ductility fibers in certain proportions. The above hybrid design concept was also proven by

experiments as shown in Fig.20(b). Based on above hybrid concept of hybrid fibers, the other two hybrid


methods were developed [6,25]

, which hybridizes fibers with conventional structural materials including steel

wires and steel bars. The hybrid basalt and steel wires FRP can achieve initial high modulus, secondary

stiffness and relatively ductility meanwhile the self-weight will not increase obviously which can still

benefit application in long-span structures (Fig.21(a)). Fig.21(b) shows a hybridization between fibers and

steel bar, which is majorly applied for RC structures. By this method, a stable secondary stiffness can be

realized which guarantees structural ductility and benefit structural damage controllability and

recoverability under moderate to large earthquake.

(a) Concept design (b) Experimental results

Fig. 20 Hybridization of three types of fibers

0 5000 10000 15000 20000 25000 30000 35000

0

100

200

300

400

500

600 B20

Str

ess

(MP

a)

Strain ()

M2

M4

M8

M10

Theoretical

Steel yield

FRP rupture

(a) (b)

Fig.21 Hybridization of basalt fibers with conventional steel

3.2 Enhancement of fatigue behavior

To further investigate the advantages of hybrid FRP aside from their contribution to the basic mechanical

properties, the fatigue behavior of hybrid basalt and carbon, carbon and glass FRP sheets were tested. It can

be seen from Fig. 22 that the fatigue strength of BFRP sheet is significantly improved through hybridizing

basalt and carbon fibers with the volumetric ratio of 1: 1. After hybridization, the hybrid B/CFRP

composites can maintain the 2 million cycles without fracture (Fig. 22) at 70% of the maximum stress

(amplitude R=0.1), which is approaching the fatigue strength of CFRP sheets (77%). This result indicates

the fatigue performance of BFRP can be designed through hybridization according to the structural

requirement and the enhancement of fatigue strength is effective. However, the hybrid G/CFRP sheets show

even lower fatigue strength than GFRP sheets, which is mainly caused by the week bonding between glass

高延性纤维高弹模纤维高强度纤维

ε

σ

高弹模纤维断裂

⊿f (控制点)

高延性纤维断裂

超过

2～3％延性

高强度纤维断裂应变强化

εf εu

fy0

fy

fm

εy0 εy

εm

钢筋卸载

卸载

HM fibers HD fibersHS fibers

Fracture of HM fibers

Strain hardening

Unloading

Unloading

Steel

Ductility>2-3%

Fracture of HS fibers

Fracture of HD fibers

0

200

400

600

800

1000

1200

1400

1600

0 5000 10000 15000 20000 25000 30000

Str

ess

(MP

a)

Strain (με)

系列5

B-1

B-2

B-3

B-4

B-5

B/S40%-

1B/S40%-

2B/S40%-

3B/S40%-

4B/S40%-

5

Steel wire

BFRP

B/SFRP 40%


fibers and carbon fibers [9]

.

Fig.22 S-N relationship under cyclic loading

3.3 Enhancement of tensile properties under elevated temperatures

Fig.23 Hybrid effect on FRP under high temperature

To clarify the hybrid effect on FRP under elevated temperatures, the hybridization of carbon and basalt

FRP, and carbon and E-glass FRP was tested under the temperatures up to 200℃. The tests results show

that hybridization contributes the reduction of dispersion of tensile strength of CFRP at high temperatures,

which means the strength become more stable and can be used more sufficiently in the design (Fig. 23) [26]

.

Fig.24 Tensile properties of FRP with different resin

It is shown that the thermal properties of the resin greatly affect the properties of FRP under elevated

temperatures. Thus, to enhance the properties of FRP under elevated temperatures, it should be ensured that

the matrix of FRP have good high-temperature performance. The research team studied the

high-temperature performance of FRP up to 500℃with different resins, phenolic-based (TG-1009) and

40%

50%

60%

70%

80%

90%

100%

110%

0 1 2 3 4 5 6

max

str

ess/

tensi

le s

tren

gth

Log of number of cycles（LogN）

CFRP

GFRP

BFRP

C/GFRP

C/BFRP

S=1.011-0.042logN

55% fu

74% fu

1C1-FRP

0

1

2

3

4

5

6

0 40 80 120 160 200

Temperature (OC)

Tensile

strength (GPa)

0

20

40

60

80

100

120

Ratios of

average tensile

strength (%)

1EG1C1-FRP

0

1

2

3

4

5

6

0 40 80 120 160 200

Temperature(OC)

Tensile

strength (GPa)

0

20

40

60

80

100

120

Ratios of

average tensile

strength (%)

2B1C1-FRP

0

1

2

3

4

5

6

0 40 80 120 160 200

Temperature (OC)

Tensile strength

(GPa)

0

20

40

60

80

100

120

Ratios of

average tensile

strength (%)

0

1000

2000

3000

4000

5000

0 100 200 300 400 500 600

Temperature (OC)

Ten

sile

str

engt

h (M

Pa)

FRP(FR-E3P)

CFRP(TG-1009)


epoxy resin. The results shown in Fig.24 indicate that although the tensile strength of FRP with TG-1009

resin is not as high as the FRP with epoxy resin at room temperature, the FRP with TG-1009 resin can

maintain the room-temperature tensile strength up to 300℃ which is 35% higher than the FRP with epoxy

resin.

Based on above studies, the models for predicting high temperature properties of FRP were proposed as

follows, which can represent the strength degradation of FRP below the temperature of decomposition [27]

.

0 0

1 1 1( ) tanh ( / 2) ( )

2 / 2 2r g r

T T TT

σr is the residual strength, σ0 is the strength at room temperature, ΔT is the temperature variation of the

glass transition region of the polymer matrix, Tg is the glass transition temperature, and T represents the

temperature.

Aside from evaluation and prediction of FRP under elevated temperatures, the design theory based on the

residual strength of FRP is still under developing. The FRP performance under high temperatures and

under the fire should be further investigated and accumulated to guide the application in structures.

3.4 Advancement of mechanical properties of BFRP under severe environment

(1) freeze-thaw cycles[12]

（a）tensile strength (b) elastic modulus (c) failure strain

Fig.25 tensile characterization of hybrid FRP sheets versus freeze-thaw cycles

As can be seen from Fig. 25, hybrid FRP sheets show a better freeze-thaw cycling resistant capacity than

homogeneous FRP sheet. There were no significant decreases in ultimate strength and modulus of elasticity

within 200 cycles. About 10% reduction was found in ultimate strain of 50 and 100 cycles exposed 1C2B

specimens, but there were nearly no decreases in 150 and 200 cycles exposed specimens. 1C1B performed

better than 1C2B FRP sheets under freeze-thaw cycling condition. Overall, there are higher COV values of

exposed specimens than the control ones. This may due to the non-uniform impact on the coupons during

freeze-thaw cycling test. Hybrid FRP sheets have lower COV than the corresponding homogeneous CFRP

and BFRP sheets after exposure, which indicates that the hybrid of fibers could contribute to the stability of

mechanical properties of FRP sheets after being exposed to freeze-thaw cycling.

(2) Under salt solution with prestressing

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

0 50 100 150 200 250Freeze-thaw cycles

Ult

imat

e st

ren

gth

1C1B 1C2B

0.9

0.95

1

1.05

1.1

1.15


Ela

stic

mo

du

lus

1C1B 1C2B

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1


Ult

imat

e st

rain

1C1B 1C2B

80%

85%

90%

95%

100%

1 2 3

BFRP CFRP B/CFRP B/SFRP

Control specimens 0, 120days 0.3fu, 120days

Tens

ile s

tren

gth

rete

ntio

n

0%

2%

4%

6%

8%

10%

1 2 3

BFRP CFRP B/CFRP B/SFRP

Control specimens 0, 120days 0.3fu, 120days

CV

of

ten

sile

str

eng

th


Fig. 26 tensile strength degradation of hybrid FRP Fig.27 CV of tensile strength of hybrid FRP

Aside from the BFRP tendons under salt solution, the two types of hybrid FRP tendons as well as CFRP

tendons were tested to identify hybrid effect and the potential enhancement in comparison to BFRP. The

test results of the tensile strength retention with respect to stress level after 120 days aging are shown in

Fig.26. It apparently shows that the applied stress accelerated the strength degradation of different kinds of

FRP tendons, among which CFRP tendons exhibit the strongest resistance to salt corrosion, followed by

B/CFRP, BFRP, whereas the degradation of B/SFRP is largest. The strength degradation of B/CFRP is quite

similar to that of CFRP and smaller than that of BFRP, for the specimens without applied stress, which may

be contributed by the positive hybrid effect of basalt and carbon fibers. However it also shows a similar

drop of strength to BFRP, for the specimens with applied stress, in which no positive hybrid effect on

lowering degradation rate can be found. For B/SFRP tendons, much larger degradation of strength can be

observed in comparison to CFRP, BFRP and B/CFRP, which indicates the steel wires corroded in B/SFRP

tendons perform an important role in strength degradation. However, no clear relationship between the CV

of tensile strength with respect to applied stress can be observed as shown in Fig.27.

4. Innovative application technologies for structures with BFRP

Based on above fundamental studies, the BFRP and the relevant hybrid FRP composites were investigated

to realize safety and sustainability in various civil and transportation engineering. The following will

summarize the major applications.

4.1 BFRP smart bar for structural health monitoring

The self-monitoring BFRP smart bar is shown in Fig.28. It is constructed by putting the distributed optic

sensors in the manufacture process of the BFRP bars which make the bar be capable of self-monitoring,

self-diagnostic. The stability and durability and its mechanic property of this smart bar can adapt to the

harsh serving condition of bridge, pavement and tunnel, it can provide an effective monitor and evaluation

for the safety operation of these transportation facilities [28-30]

.

The smart bars can be embedded in concrete beams and they can monitor the structural state during the

entire serving life (static load tests). Fig. 29 shows the strain distribution along the bar after beam bottom

cracked, the result fit with the experimental phenomena, the strain peak appears at the cracks. As shown in

Fig. 30, in the reinforced concrete pavement, smart bars can effectively measured contraction deformation

within 28 days after pouring concrete day and sensors in the structure have been able to work stable after

structure forming. The smart bars are also expected to apply in monitoring the performance of asphalt

concrete pavement. At the same time, the research team will use the smart bars to monitor the deformation

of hoop and longitude direction of the tunnel by embedding the smart bars at these directions (Fig.31). It

provides a new thought of how to solve the monitoring hardness under complex geological environment.

-200

0

200

400

600

800

1000

0.00 0.30 0.60 0.90 1.20 1.50 1.80

距离m

应变

µε

40kN

50kN

60kN

70kN

90kN

cracks

Distance (m)

Str

ain

(με)


Fig.28 BFRP smart bars Fig.29 RC beams with BFRP smart bars

Fig.30 Pavement with BFRP smart bars Fig.31 Application of BFRP smart bars in tunnel structures

4.2 BFRP and hybrid FRP cables for long-span bridges [31-34]

To meet the world wide need for long-span bridges over the bay or strait like the Su-Tong Bridge, Hong

Kong Stonecutters Bridge, Qiongzhou Strait projects, Messina Strait Bridge (Italy), Gibraltar Straits Bridge

(Spain, Morocco), etc., it has become a research hotspot that how to use the advanced FRP material as a

substitution for the traditional materials. The research team proposed the use of BFRP and hybrid FRP

cables as a replacement of the traditional steel cables as to achieve the high-performance and balance the

economic issue. Traditional steel wire (strand) will affect the overall performance of bridge because of its

shortcomings like heavy weight and is prone to corrosion when in the span of 1000 meters. Some scholars

proposed that using carbon FRP cable can solve above problems, but the large-scale application is limited

because of its high price. Also, the carbon FRP cable is more sensitive to the wind effect because of its high

strength and low density. Based on this, the research team put forward a method of using basalt-carbon

fiber composite cable to achieve the high performance. The research results indicate that: (1) the hybrid

basalt-carbon FRP cable in the 1000m span cable-stayed bridge can achieve the excellent static and

dynamic performance like CFRP cable but the price costs only 68% (Fig. 32,33); (2) the aerodynamic

stability performance of the hybrid basalt-carbon FRP cable is more superior than the CFRP cable, also we

can increase the cable’s damping to achieve the smart performance like self-damping by sectional design

based on the different attributes of two FRP inside the cable (Fig.34); (3) the self-damping cable shows

lower resonance amplitude and stress amplitude under indirect excitations comparing to the CFRP cable

and steel cable, which benefits the safety and long-term performance of the cable (Fig.35).

In addition, the research team has also developed a basalt fiber-steel wire FRP cable which is suitable for

the bridge with a span less than 2000m span, which have a better performance-price ratio. The author also

analyzed and evaluated the applicability of four types of cables in the span range from 1000m to 10000

meters including two composite cable mentioned above and pure BFRP cable and CFRP cable based on the

utilization ratio of each material (Fig. 36). Meanwhile the FRP cable can also be combined with the

distributed optic sensors. The design is of great importance to the real-time monitoring and real-time

control of cable under traffic load and wind load (Fig.37).

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

0 5 10 15 21 26 31 36 41 46 51 56 62 67

距离/m

应变/µε 7天

14天

28天

14 days

28 days

7 days

Distance (m)

Stra

in (μ

ε)


Fig. 32 Static behavior of cable-stayed bridge with a span of 1000m Fig.33 resonance between cables and deck

40134

252

40

200

Viscoelastic

material Outer cable

Inner cable

500 m544 m

SymmetryLength=575 m

40

In plane damper

Out of plane damper

40

Fig.34 Self-damping hybrid FRP cable

Fig.35 Response under external excitation Fig.36 Applicable length of different FRP cables

Fig.37 Design of self-sensing FRP cable

4.3 Prestressed BFRP for structural strengthening[35-36]

Since most of the fiber composite has low elastic modulus than steel, and the existing structures have

already been under load condition before strengthening, the strength of the FRP cannot be fully used

because it only deformed with the original structure under secondary loads, which result in material waste.

0

200

400

600

800

1000

1200

1400

0 10 20 30 40 50 60

Vertical displacement of mid-span (m)

Dis

trib

ute

d lo

ad (

kN

/m)

with steel cable with CFRP cablewith BFRP cablewith hybrid B/CFRP cable

0

0.5

1

1.5

2

2.5

3

3.5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

The order of natural frequencies

Th

e n

atu

ral

freq

uen

cie

s (H

z) Steel cable

CFRP cable

BFRP cable

Hybrid B/CFRP

cableEntire bridge

dd

rr

vv

vn

0

1000

2000

3000

4000

5000

6000

0 50 100 150 200Amplitude of external excitation (mm)

Am

plitu

de

of

cab

le v

ibra

tio

n (

mm

)

Steel cable

CFRP cable

Hybrid B/CFRP cable

Hybrid B/CFRP cable with self-damping

0.00

1.00

2.00

3.00

4.00

5.00

6.00

500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Horizantal length of cable (m)

λ

HS steel cable CFRP cable B/CFRP 25% cable

B/SFRP 20% cable B/SFRP 30% cable B/CFRP 50% cable

BFRP cable

2

λ =1.782

Long-gage fiber optic sensor Basalt fiber

Matrix

Fiber optic sensor


Based on this, a prestressing technology of FRP sheet was proposed in order to improve the material

utilization. The fiber sheet without be impregnated with the matrix has low tensile strength, so the applied

prestressing cannot be effectively imposed on the structure. On the other hand, if the sheet is impregnated

in the matrix and hardened, the fiber sheet is difficult to attach to the structure because of its curving

surface after matrix hardened. To solve this conflict and improve the utilization efficiency of fiber sheet, the

research team proposed the dry hybrid carbon-basalt fiber sheet to form a new composite sheet in order to

achieve the high strength tensile of dry hybrid fiber sheet (Fig. 38). The different hybrid ratios were tested

and compared and the results show that tensile strength of dry carbon fiber sheet increase from 30% to 54%

of the FRP, which guarantee the implementation of high prestressing on the fiber sheet. With this method, a

flexural strengthened beam with one layer of basalt fiber plus three layers of carbon fiber was tested which

endures 33% of the tensile prestressing of dry fiber. The results are shown in Fig. 39, It can be seen that the

prestressing play an important role in improving the strength and post-stiffness of structure.

0

20

40

60

80

100

0 5 10 15 20 25

Displacement （mm）

Load(k

N)

With 33%-prestressed 1layer Basalt and 3layers carbon fiber sheets

With non-prestressed 1layer

Basalt and 3layers carbon

fiber sheets

Without fiber sheets

Fig.38 Tensile strength of 2m long fiber sheets Fig.39 L-D curves of prestressed strengthening beams

Basalt fiber sheet can achieve the pre-tension by not only hybridizing with carbon fiber sheet but also by

hybrid with steel wires (B/SFRP) with a small diameter (also called piano wires), which can improve the

overall stiffness and the cost will not increase much (Fig. 40). As shown in Fig.34, the stiffness of two

layers of basalt fiber sheet can be significantly improved to like three layers by hybridizing 20% of piano

wires in volume. The tests on the beams prestressed strengthened with this type of basalt-steel wire sheet

show that the crack load and yield load are both increased as show in Fig. 41.

Fig.40 L-D curves of B/SFRP sheet Fig.41 Beam prestressed strengthened with B/SFRP sheet


Fig. 42 External bonded prestressing BFRP strengthening system

An innovative strengthening method by prestressing BFRP tendons was also investigated as shown in Fig.

42, in which BFRP tendon was externally bonded on the bottom of the beam by epoxy resin. A special bond

process was developed to guarantee reliable interfacial bonding as shown in Fig. 43.

Fig.43 Developed bond process

(a) Crack (b) Capacity

Fig.44 Crack and capacity performance of prestressing BFRP strengthening beams

The experimental results are show in Fig.44. In Fig 44(a), it is shown that the beam with 25% prestressing

BFRP tendons exhibits higher cracking load and much small crack width comparison with non-prestressing

BFRP strengthened beam and control beam. Meanwhile, up to the cracking limitation (0.2mm), the 25%


prestressing BFRP strengthened beams have double capacity than the control beam. Fig.44(b) shows the

L-D curves of beams with prestressed and non-prestressed BFRP tendons, in which prestressing BFRP

tendon strengthening contributes imporvemnt of cracking load, the stiffness before steel yielding and the

yielding load. Both figures also show that the experimental results fit well with the analytical results, which

indicates the current prestressing method can be used for design in application.

4.4 Damage controllable and recoverable structures with SFCB or partially with BFRP bars[37-38]

In order to realize damage controllability and recoverability of structures, the structural behavior under

different load magnitudes is divided into four states as shown in Fig. 45. The first state represents the

structure before yielding of reinforcement, which is corresponding to the elastic status and the status of

cracking. Within this stage, structural members have no need to repair due to their elastic behavior under

the earthquake. In the second state, the nonlinear behavior represents the structures under the moderate

magnitude of earthquake due to the yielding of steel reinforcement. In this stage, a stable secondary

stiffness of structure exhibits which benefits for the structural deformation control and rapid recovery after

damage. The third state represents the deformation ability of structure after secondary stiffness, which

requires sufficient deformation ability under large earthquake. In this state, the structure can be recovered

by replacing partial damaged members. For the fourth state, the structure is subjected to rare extremely

large earthquake and the aim is to prevent structure collapse.

Fig.45 Schematic of damage controllable and recoverable structures

Two ways are currently investigated to realize structural damage controllability and recoverability, the

structure reinforced with SFCB and the structure with hybrid BFRP and steel bars as show in Fig.46.

maxH

yH

Ultimate

Point

Serviceability

StateDamage Controllable

State

Ultimate

State

Residual Displacement h/100

H

H(δ)

hRequiring

Repair

Dilatory

Repair

No Repair

Second

Stiffness

Normal RC Flexural

Structure

Proposed Damage-

Controllable RC StructureltheoreticaH

Concrete

Cracking

Minor

Shaking

Moderate

Shaking

Major

Shaking

Dilatory

Repair

Recoverability limit


Fig.46 Two ways realizing structural recoverability

The hysteretic curves of the columns with SFCB and hybrid BFRP/steel are shown in Fig. 47 (a) and (b),

respectively. It can be seen that compared to the regular RC column, the SFCB strengthened columns show

obvious secondary stiffness and smaller residual deformation after unloading. These two characteristics are

of great importance to realize the energy dissipation, damage control and post-earthquake recovery of the

construction. Aside from the columns with SFCB, the columns with partial BFRP bars also show obviously

the stable secondary stiffness and the less residual deformation in comparison to that of the conventional

steel reinforced columns. The results further prove the proposal of the damage controllable and recoverable

structures.

(a) by SFCB (b) by hybrid BFRP and steel

Fig.47 Hysteretic curves of columns strengthened with SFCB and partial BFRP under cyclic loading

HS steel bar/FRP bar Common steel

bar

配筋纵筋

混凝土

Hybrid FRP bar：SFCB

OR

Longitudinal

reinforcement

Concrete

Hybrid

FRP bar

-50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50

-150

-100

-50

0

50

100

150

C-S14

C-B30S10

The same loading

displacement

Lo

ad(k

N)

Displacement (mm)

Different residual

displacement

BD10-E

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

-80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80変位(mm)

荷重

(KN

)

Deformation (mm)

Load

(kN

)

Yield of steel

BFRP fracture


Fig.48 Retrofitting exsiting columns by NSM BFRP bars

Above application of hybrid BFRP and steel bar for damage recoverable and controable columns can also

be used for retrofitting exsiting RC columns, which is realized by near-surface mounted BFRP bars on the

sides of the column as shown in Fig.48. The hysteretic curves also shows stable secondary stiffness and

smaller residual deformation after unloading.

Fig.48 Envelope diagram of load-deformation of BFRP NSM strengthened columns

The current research also investigated the effect of two factors controlling the strengthening effect of

columns by BFRP bars, the diameter of BFRP bars and the bonding materials, respectively. Envelope

diagram of load-deformation of BFRP NSM strengthed columns is shown in Fig.?, in which three types of

diameters (6mm, 10mm and12mm) and two types of bonding materials (E: epoxy putty and EP: polymer

cement) are considered. The results indicate that more stable secondary stiffness and more ductile behavior

of columns can be achieved by thicker BFRP bars based on the equivalent reinforcement ratio. Because the

relative slippage between BFRP and RC occurs easily for thicker bars due to their small interfacial area,

which allows more sufficient use of BFRP materials under the cyclic loading and fail by fracture of BFRP

bar. On the contrary, the columns with thinner BFRP bars, the collaborative work between BFRP and RC

column due to more reliable bonding will limit the relative slippage and lower the utilization efficiency of

inner BFRP bars (pull out of BFRP bar). The results also shows that for thicker BFRP bars, the adoption of

D6@30mm

D6@50mm

D6@100mm

15×15mm

200mm

50m

m

20mm

15mm

240m

m70

0m

m

D13

E or EP bonding

BFRP rod

BFRP sheet

荷重-変位包絡線

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

-80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80変位（mm）

荷重

(kN）

無補強(旧設計)

BD6-E

BD6-EP

BD10-E

BD10-EP

BD12-E

No strengthening

Deformation (mm)

Load

(kN

)


epoxy putty can achieve high bonding capacity and ductility with the failure mode controlled by BFPP

fracture as shown in Fig.49.

Fig.49 Pull-out test of BFRP bars with different bonding materials

4.5 BFRP profiles for sustainable structures [39-40]

The fiber sheets are usually used for the reinforcement of the existing structures; however, the FRP profiles

are more suitable for the construction of the new structure. FRP Profiles not only have fixed shape which

can be used as structural formwork, but also through the use of wet-bonding techniques, it can effectively

guarantee the reliable bond between FRP profiles and structure, which makes FRP profiles achieve full

strength, improves the bearing capacity of the structure of guarantee ductility. Based on this, the research

team has studied and developed the T-shaped basalt-carbon fiber-concrete composite beam (Fig. 50). The

hybrid BFRP and CFRP on the bottom of the girder can increase the stiffness and maintain ductility and the

shear reinforcement by BFRP can achieve sufficient shear strength and lower the cost. The tests results

(Fig.51) show that (1) comparison of results of several bonding methods, including wet bonding, dry

bonding and pre-bonded gravel, shows that each bonding method can achieve good results, in which

wet-bonding approach not only can obtain good results, but also facilitate the rapid construction; (2) the

composite beams have obvious secondary stiffness after yielding of the longitudinal reinforcement and the

ultimate load are greatly improved; (3) the hybrid of CFRP and BFRP improve the ultimate strain of CFRP,

and the layers of BFRP are directly proportional to this effect. As a result, the material utilization efficiency

is improved. In addition, the wet-bonding plus shear studs composite beams were also investigated as

shown in Fig.52, which shows not only reliable bonding of interface between concrete and FRP can be

achieved, but also superior flexural behavior under the static and cyclic loading can be realized.

CFRP: tensile

reinforcement (strength, stiffness)

BFRP: tensile

reinforcement

(ductility)

Tensile steel rebars

BFRP: shear reinforcement

Stirrup

FRP anchorage

Wet bonding

with external

resins

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Lo

ad

(K

N)

Displacement (mm)

BD10-240-E BD6-240-E

BD10-240-EP BD6-240-EP

D10(82KN)

D6（38KN）


Fig 50 Schematic of fiber profiles-concrete composite beam

Fig.51 Wet-bonding U shape FRP-RC beams

Fig.52 Capacity of the beams with different bonding methods

5. Summary and suggestions

This paper summarizes the recent research and application of basalt fibers and the composites in the field of

civil and transportation infrastructure in order to enhance the structural safety and sustainability. It is

clarified that basalt fibers have excellent compatibility with matrix resin and can be hybridized with steel

wires, steel bars, or other fiber materials achieving a prominent hybrid effects shown in short-and long-term

mechanical properties, fatigue resistance, high temperature performance, and etc. Aside from the general

structural reinforcement by BFRP composites, the basalt FRP and hybrid FRP are also able to play an

important role in smart structures, long-span bridges, damage controllable and recoverable structure,

light-weight and sustainable structures, and etc. Based on the above study, some recommendations on the

future development are proposed as follows:

(1) Accelerating development of new basalt fibers and BFRP products

In order to be better and faster in promoting wider fields of applying basalt fiber composites, the research

and development of basalt fibers and the related FRP products should be accelerated to solve current

problems, bridge gaps between research and application, and lower the cost.

(2) Strengthening basic research

Currently, since the application of basalt fiber composites is in precede of basic research, in order to have a

better and more scientific application, the systematic study of the short- and long-term, static, dynamic,

extreme environmental properties of basalt fiber and its composites should be strengthened to establish the

0

50

100

150

200

250

300

350

0 5 10 15 20 25 30 35Displacement (mm)

Load (

kN

)

FRP-RC-0.29%FRP-RC-0.43%FRP-RC-0.77%

FRP-RC-1.20%

FRP-RC-1.73%RC-2.38%

0 20 40 60 80 1000

50

100

150

200

250

300

350

400

Lo

ad

/kN

Deformation /mm

B2

B3

B4

B8


corresponding theoretical model and design methods to guide the practical application.

(3) Rational use of basalt fibers and the composites

Basalt fibers and the composites have many advantages, but there are shortcomings as well. They should be

developed objectively and used dialectically. Thus, a systematically comparison and combination of the

advantages and weakness among BFRP and CFRP, GFRP and AFRP should be conducted seriously,

through which full use of advantages and healthy development of different fiber composites in engineering

can be expected.

Acknowledgement

The writers gratefully acknowledge the financial supports from the National Program on Key Basic

Research Project (973 Program, No. 2012CB026200), the Jiangsu NSF (No.BK2010015), and

acknowledge Zhejiang GBF Basalt Fiber Co., Ltd. for their providing related data sources.

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